var isSameTree = function(p, q) {
    if(p==null&&q==null){
        return true
    }else if(p==null || q==null){
        return false
    }else if(p.val!==q.val){
        return false
    }
    return isSameTree(p.left,q.left)&&isSameTree(p.right,q.right)
};